Heating apparatus



Feb. 12,1946. H; J, DE; N. MccoLLuM Erm, 2,394,627

HEATING APPARATUS Filed Oct. 21, 1942 -I 2 Sheets-Sheet 1 2a 1 f A@ Fb. 12, 19'46. H. J. DE N. McQLLUM s-rm.l y 2,394,627 v HEATING APPARATUS Filed oct. 21, 194 2 sheets-sheet 2 v of the heater.

Patented Feb. 12, 1946 UNITED STATE s PATENT orFlcE l HEATING APPARATUS McCollum, deceased Application October 21, 1942, Serial No. 462,788

3 Claims.

Our invention relates to` heating apparatus, and more particularly to heaters of the internal combustion type, especially adapted for, but not limited to, use in aircraft.

In heaters of the internal combustion type, it is common to provide finned heat transfer means for transferring heat from the products of combustion to Ventilating air directed over the heat transfer means by a ram or blower, or other air circulating means. The heated products of combustion are originally directed against the iins at one end of the heat transfer means and where the hot products of combustion first come in contact with the ilns, these fins are raised to a temperature which is much in excess of the temperature of other portions of the iins and particularly that portion adjacent the outlet end There is ai practical limit to the temperature to which any part of the ilns can be heated and in the prior art heaters it was necessary to operate large portions of the fins at temperatures' materially below this vlimit in order that the hot spots in the fins should not exceed this limit.

An -object of our invention is to provide heating apparatus of the internal combustion type in which local hot spots are eliminated and the heat transfer means is heated to a substantially uniform temperature throughout its length.

Another object of our invention is to provide heating apparatus wherein the temperature range between different parts of the heat 'transfer means is reduced lto a minimum and stresses and strains caused by great variations in temperature of different portions of the heat transfer means are avoided.

Another object of our invention is to provide heating apparatus wherein the lentire area of Ithe heat transfer means can be maintained at substantially the temperature limit dictated by the material of which .this transfer means is made and the heating apparatus can furnish the maximum heat output for a given size and kind of material.

Another object of our invention is to provide new and improved heating apparatus which is extremely light in weight and compact and ha a high heat output. v

Other objects and advantages will become apparent as the description proceeds.

In the drawings:

Fig. 1 is a view showing a longitudinal section through a preferred embodiment of our invention;

Fig. 2 is a view showing a partial, transverse section taken on the line 2-2 of Fig. 1:

Fig. 3 is a fragmentary view in longitudinal section and illustrating a feature of our inven-y tion on an enlarged scale;

Fig. 4 is a view showing a partial longitudinal section through a modified form or our invention;

Fig. 5 is a view showingk a partial, transverse section taken on the line 5-5 of Fig. 4; and

Fig. 6 is a fragmentary view in longitudinal section showing a feature of our invention on an enlarged scale.

The embodiment disclosed in Figs. 1, 2 and 3 comprises a combustion chamber I0 supplied with Aa combustible mixture by a carburetor I2 having an outlet end communicating with the combustion chamber by way of a burner tube I4 which serves to give the combustible mixture a whirle ing motion as it enters the combustion chamber. A fuel supply pipe I6 furnishes either fuel or' a rich mixture of fuel and air to the carburetor i2 and has outlet openings I8 located in the restricted throat oi' this carburetor. The right-hand lend 2G of the carburetor is supplied with air from the heater inlet 22 which is adapted to be connected with a ram, blower, or other air circulating means.

One or more electrical igniters 24 ignite the combustible mixture when it first enters the combustion chamber I0. These igniters are usually connnected to a source of current supply by way of a thermostatic switch which is responsive to the temperature 'of the heater andwhich disconnects the igniters from their current source when the heater attains normal operating temperature. v

The re-igniter 26 is provided to insure maintenance of combustion after the igniters 24 have A been cut off from their current source.

pinched together, as indicated at 36 and 38 in Fig. 1, or are otherwise suitably sealed to close the ends of the gas passages 34.

i A muilier `40 is located in the tubular heat exchanger 30 and has atsheet metal shell 42 containing, a quantity of sound absorbing material 44, such as glass wool or stainless steel wool. The shell 4 2 is provided withfopenings 46 formthe shell and the gas passages, whereby sound entrainedA in the products of combustion may 'pass into the interior of the muiier shell and be absorbed by the glass `wool therein. A sheet metal cap 48 is welded or otherwise secured to yone end of the muier shell d2 and cooperates therewith to form a heat insulating and resonance chamber d which is acoustically ccnnected to the interior of the muilier shell by openings 52.

The lefthand end of the tubular heat exchanger im is closed by a plate 64 sha/pcd to form an outlet chamber te into which the cooled products-of combustion flow from the lefthand ends of the passages 34. These cooled gases or products of combustion are discharged to the atmosphere through an outlet tting 58 and any suitable exhaust pipe attached to the threaded end l ofthisiltting.

A cylindrical sheet metal casing 82 surrounds the heat exchanger and cooperates therewith to form a passage for Ventilating air between and around the hollow ns 32. A sheet metal cone Il connects the righthand end of this casing 82 with the heater inlet 22 which supplies the ventilating air flowing between this casing and the heat exchanger 30. Thisventilating air absorbs heat from the heat exchanger and the heated Ventilating air is discharged from the lefthand end of the casing B2 into the aircraft cabin or other space to be heated or into a system of ducts for conducting this Ventilating air to selected locations. Y

The hot gases flowing from combustion chamber I0 first contact the righthand ends of the hollow finsl and tend to heat these ends of the fins and particularly the bases B8 thereof to a temperature higher than the remaining portions 'of the fins. We have provided special means to prevent this portion of the fln bases from attaining a temperature higher thanthe remaining portions of the fins. In Fig. 1, .this means assumes the form of ank annular sheet metal baille 88 which is welded or otherwise secured to the interior of the cylindrical casing 82 and which serves to'direct the ventilatingair more intensively against the righthand end of the fins and particularly against the base portions of this righthand end; This baille is curved in cross section, as more clearly shown in Fig. 3, and the inner edge of the baille closely approaches the tips of the ilns.

The curvature of the baille 88 changes thedirection of. the Ventilating air flow with a mimmum `of resistance to this flow and directs the Ventilating air against the bases of the fins at an angle more nearly approaching the perpen-A dicular. At the same time, the rate ofilow 'of the Ventilating air is materially increased where it is forced against the'flns and crowded between these fins andthe-inner edge of the baille 68. The increased angle of attack of the air against the iin surface and the increased speed of this air produce an increased scouring action at and adjacent the baille 68 and greatly increase the rate of heat transfer at this point from the fins and particularly the fin bases tov the Ventilating air. This increased rate of heat transfer from the fins to the Ventilating air prevents the temperature of the adjacent portions of the fins from Vrising above the temperature of other portions aseasav perature and, since this temperature may be the practical limit for the material used, our novel heater is capable of producing a heat output equal to the theoretical maximum for any given size and style of heater.

In the preferred arrangement, as shown, the mumer 40 extends completely across the open central portion of the tubular member tu so as to cause all of the combustion gases to flow through the passages 34 inside of the ilns 32 formed by the deep longitudinally extending corrugations of the wall, such combustion gases being deflected outwardly to such passages 3d by the backwardly4 tapered shell of the muiiier. The baiile 88 carried by the casing outside of the tubular member 3@ is located in such position with respect to the muiiier d0 that the cold air on the outside of said member 30 is directed into contact with the outer face portions of the corrugations at approximately the same point 1ongitudinally of the heater as thatat which the hottest part of the combustion gas stream contacts the inner face portions of the corrugations.

' The result is that there is a highly eiective transfer of heat from the limited quantity of the combustion gases to the comparatively much greater quantity of the cold air to be heated, serving to protect the metal wall portions from being burned out even though such wall portions b e -of comparatively very thin metal. 'Ihis arrangement provides for a. maximum heat transfer in proportion to the weight of the sheet metal jacket v of said heat transfer member 30 which feature is, of course, of very great importance in connection with a heater for use for aircraft.

The modification shown in Figs. 4, 5 and 6 is identical with the heater previously described, except that the sheet metal casing vfits more closely about the heat exchanger 30 and a different type of baille is used to direct the ventilating air into more intimate contactv with the iins. In the embodiment of Figs. 4, 5 and 6, the cylindrical casing 62' is of slightly smaller diameter than the cylindrical casing 82 and ts 'more closely about the tips of thens of the heat exchanger 30. The inlet or righthand end of the casing 82 is connectedto the heater inlet 22 by a sheet metal cone 8l' which is identical with the cone 64, except that the enlarged end of the cone 8l' is made of appropriate size to fit the smaller diameter of the casing'.

Ventilating air entering the inlet 22 is directed through cone 64' into the inlet end of casing 62' and starts ilowing between the righthand end of the heat exchanger 30 and the cylindrical wall of the casing 62'; The annular baille 88' defiects this Ventilating air toward the heat exchanger 30 into more intimate contact with the fins thereof and particularly with the bases of these fins to increase the rate of heat transfer between the Ventilating air and fins over that portion of the heat exchanger' which is first contacted by ilshe hot gases from the combustion chamber 0.

The baille 68' is curved in cross section, as most clearly indicated in Fig.'6. and has a serrated inner edge providing fingers 10 which extend between the outer portions of the fins 32. y

These fingers 10 have lateral edges parallel to the side walls of the fins 32 and spaced slightly therefrom to permit thin lms of air to flow between the edges of the fingers 10, and the side walls of the fins. The bottoms 12 of the recesses formed in baille 68' between adjacent fingers are also spaced from the tips of the fins 32 and permit some air to flow between these bottoms and the iin tips to absorb heat therefrom, The.1

ends 14 of the fingers 10 are spaced from the bases 66 ofthe uns and most of the Ventilating air rushes through the restricted passages formed between these finger ends and the fin bases.

Ihe rush of Ventilating. air adjacent the 1in bases scours these bases and the lower portions of the side walls of the fins and absorbs great quantities of heat therefrom. This prevents the creation of hot spots in that portion of the heat s exchanger which is first contacted by the hot products oi combustion. The elimination of hot spots in the heat exchanger is effected with a minimum of additional parts and a minimum increase in weight of the heater; Stresses and strains in the heat exchanger are thereby avoided, but the greatest-advantage is the material increase in the total heat output which much more than offsets the slight increase in weight and the slightly greater resistance of the heater to the iiow therethrough of the Ventilating air.

Because the heating apparatus embodying-our invention can be made extremely compact. and light in weight'for a given heat output, our heating apparatus is particularly adapted for use in aircraft and under other conditions where savings in weight and size are of particular importance. Our heating apparatus,- however, is not limited to' such use, but is 'equally adapted for other purposes. Furthermore our invention is vnot to be understood as limited to the details shown and described, but'may as e numerous other forms and is-to be construe as including all modiiications and variations falling within the scope of the appended claims.

We claim: 1. In a heating apparatus of the class described.

the combination of a heat transfer memberl hav-v ing its wall deeply corrugated longitudinally,`

the outside passages between'the corrugations at substantially the same position longitudinally of the heater as that at which the heated gases are directed into the inside passages for eifecting a maximum transfer of heat from the wall to said air.

2. In a heating apparatus of the class described, the combination of a heat transfer member having its wall deeply corrugated longitudinally, means for delivering heated gases forwardly into said member, backwardly tapered means in said member adapted to direct said heated gases outwardly into the inside passages between the corrugations, a casing surrounding said member in outwardly spaced relation thereto, means for delivering air to be heated for- .wardly through said casing about said member, and a baille mounted on the inner face of said casing in close proximity tothe outer edges of said corrugations and positioned at such distance along .the heater as to direct the air into the outside passages between the corrugations at substantially the same position longitudinally` of the heater as that at which the heated gases are directed into the inside passages between the corrugations.

3. In a heating apparatus of the class described, the combination of a heat transfer member having its wall deeply corrugatedl longitudinally, means for delivering heated gases forwardly into s aid member, backwardly tapered means in said member adapted to direct said portions of the passages, such baille being posi- -tioned at such distance along the heater as to direct the air into said outside passages at substantially the same position as that at which the lheated gases are directed into the inside pas sages 'between the corrugations.

HENRY J. DE N.

LYNN A. WILLIAMS, JR. 

